The reason why people "pile on the pounds after quitting smoking could lie in our DNA”, the Daily Mail has said. The newspaper says that research has found a “fat-burning gene” that is activated when exposed to cigarette smoke.

The research behind this story demonstrated that the AZGP1 protein, which is involved in the breakdown of fats, is more active in the large airways of smokers than in nonsmokers. Although this analysis may give a possible explanation of why smokers’ bodies may gain less fat, its implications are quite limited given the numerous serious health problems associated with smoking.

This research should not be used as a reason to continue smoking, regardless of whether smoking keeps weight off for some people. The best way to lose weight and stay healthy is through a balanced diet and regular exercise.

Where did the story come from?

This research was conducted by Dr Holly Vanni and colleagues of the Division of Pulmonary and Critical Care Medicine and Department of Genetic Medicine, Cornell University. The research was funded by the Will Rogers Memorial Fund (a medical research and education foundation) and published in the peer-reviewed medical journal Chest.

What kind of scientific study was this?

This was a laboratory study investigating why smokers generally weigh less and have less body fat than nonsmokers, and why they tend to gain weight following smoking cessation.

The researchers theorised that smoking may lead to increased production of a fat-reducing protein called alpha2-zinc-glycoprotein1 (AZGP1) in the lining of the airways. The protein has been shown to reduce body fat in mice, even when their food and water intake remained the same. The same protein has also been found in the urine of cancer patients suffering from severe weight loss.

Samples were taken from the linings of the large airways of 55 otherwise-healthy smokers and 37 healthy nonsmokers. The researchers used different laboratory methods to analyse and compare levels of the AZGP1 protein in these healthy nonsmokers and healthy smokers.

What were the results of the study?

Laboratory analysis of the large airway lining samples demonstrated that smokers had significantly higher levels of messenger RNA (genetic material used in protein production) encoding for AZGP1 synthesis.

Analysis of airway tissue samples demonstrated that smokers had increased production of the protein AZGP1 compared with nonsmokers, and that there was increased production of AZGP1 in the secretory cells of smokers, plus the cells of their nervous and hormonal systems.

What interpretations did the researchers draw from these results?

The researchers conclude that, as AZGP1 is involved in the breakdown of body fat, the greater quantities present in the airway lining of chronic smokers may represent a possible mechanism behind their lower weights.

What does the NHS Knowledge Service make of this study?

This research has demonstrated that a protein, AZGP1, which is involved in the breakdown of fats, is more concentrated in the lining of the large airways of smokers compared to nonsmokers.

Although this analysis may give a possible physiological explanation of why smokers’ bodies may be more easily able to keep off body fat, its implications appear to be quite limited, and the numerous health risks of smoking are widely known.

The best way to lose weight and stay healthy is through a balanced diet and regular exercise. Regardless of whether smoking keeps the weight off for some people, this research should not be used as a reason to continue smoking.